In the art, many thermoplastic polymers require stabilization upon exposure to high temperatures since a polymer per se is not generally stable against discoloration or degradation when exposed to elevated temperatures. Certain additives have been found that are suitable for stabilizing thermoplastic polymers when exposed to elevated temperatures. Particularly useful are certain phosphites which have been disclosed as stabilizing thermoplastic polymers and in particular the case of aromatic polycarbonate resins as set forth in U.S. Pat. No. 3,305,520. The particular phosphites were found to be suitable for stabilizing clear polycarbonate resins against discoloration due to heat aging. In addition to phosphites, other materials in combination with phosphites such as tetraaryl tin compounds disclosed by Canadian Pat. No. 727,700 have also been useful.